Semiconductor image sensor

ABSTRACT

A BSI image sensor includes a substrate including a front side and a back side opposite to the front side, a plurality of pixel sensors, an isolation grid disposed in the substrate and separating the plurality of pixel sensors from each other, a reflective grid disposed over the isolation grid on the back side of the substrate, an a low-n grid disposed over the back side of the substrate and overlapping the reflective grid from a top view. A width of the low-n grid is greater than a width of the reflective grid.

PRIORITY DATA

This application is a continuation of U.S. patent application Ser. No.16/706,189, filed on Dec. 6, 2019, entitled of “SEMICONDUCTOR IMAGESENSOR”, which is a continuation of U.S. patent application Ser. No.15/928,748, filed on Mar. 22, 2018, entitled of “SEMICONDUCTOR IMAGESENSOR”, which claims priority of U.S. Provisional Patent ApplicationSer. No. 62/579,474 filed Oct. 31, 2017, the entire disclosure of whichis hereby incorporated by reference.

BACKGROUND

Digital cameras and other imaging devices employ images sensors. Imagesensors convert optical images to digital data that may be representedas digital images. An image sensor includes an array of pixel sensorsand supporting logic circuits. The pixel sensors of the array are unitdevices for measuring incident light, and the supporting logic circuitsfacilitate readout of the measurements. One type of image sensorcommonly used in optical imaging devices is a back side illumination(BSI) image sensor. BSI image sensor fabrication can be integrated intoconventional semiconductor processes for low cost, small size, and highintegration. Further, BSI image sensors have low operating voltage, lowpower consumption, high quantum efficiency, low read-out noise, andallow random access.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a top view of a portion of a semiconductor image sensoraccording to aspects of the present disclosure in one or moreembodiments.

FIG. 2 is a cross-sectional view of a portion of a semiconductor imagesensor taken along a line A-A′ of FIG. 1 according to aspects of thepresent disclosure in one or more embodiments.

FIG. 3 is a cross-sectional view of a portion of a semiconductor imagesensor according to aspects of the present disclosure in one or moreembodiments.

FIG. 4 is a cross-sectional view of a portion of a semiconductor imagesensor according to aspects of the present disclosure in one or moreembodiments.

FIG. 5 is a cross-sectional view of a portion of a semiconductor imagesensor according to aspects of the present disclosure in one or moreembodiments.

FIG. 6 is a flow chart representing a method for manufacturing asemiconductor image sensor according to aspects of the presentdisclosure.

FIG. 7A through 7H illustrate a series of cross-sectional views of aportion of a semiconductor image sensor at various fabrication stagesconstructed according to aspects of the present disclosure in one ormore embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of elements and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper”, “on” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As used herein, the terms such as “first”, “second” and “third” describevarious elements, components, regions, layers and/or sections, theseelements, components, regions, layers and/or sections should not belimited by these terms. These terms may be only used to distinguish oneelement, component, region, layer or section from another. The termssuch as “first”, “second” and “third” when used herein do not imply asequence or order unless clearly indicated by the context.

As used herein, the terms “approximately,” “substantially,”“substantial” and “about” are used to describe and account for smallvariations. When used in conjunction with an event or circumstance, theterms can refer to instances in which the event or circumstance occursprecisely as well as instances in which the event or circumstance occursto a close approximation. For example, when used in conjunction with anumerical value, the terms can refer to a range of variation of lessthan or equal to ±10% of that numerical value, such as less than orequal to 5%, less than or equal to 4%, less than or equal to 3%, lessthan or equal to 2%, less than or equal to 1%, less than or equal to±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. Forexample, two numerical values can be deemed to be “substantially” thesame or equal if a difference between the values is less than or equalto ±10% of an average of the values, such as less than or equal to ±5%,less than or equal to 4%, less than or equal to 3%, less than or equalto 2%, less than or equal to 1%, less than or equal to ±0.5%, less thanor equal to ±0.1%, or less than or equal to ±0.05%. For example,“substantially” parallel can refer to a range of angular variationrelative to 0° that is less than or equal to 10°, such as less than orequal to 5°, less than or equal to 4°, less than or equal to ±3°, lessthan or equal to ±2°, less than or equal to ±1°, less than or equal to±0.5°, less than or equal to ±0.1°, or less than or equal to ±0.05°. Forexample, “substantially” perpendicular can refer to a range of angularvariation relative to 90° that is less than or equal to 10°, such asless than or equal to ±5°, less than or equal to ±4°, less than or equalto ±3°, less than or equal to ±2°, less than or equal to ±1°, less thanor equal to ±0.5°, less than or equal to 0.1°, or less than or equal to±0.05°.

BSI image sensor includes an array of pixel sensors. Typically. BSIimage sensors include an integrated circuit having a semiconductorsubstrate and light-sensing devices such as photodiodes corresponding tothe pixel sensors arranged within the substrate, a back-end-of-line(BEOL) metallization of the integrated circuits disposed over a frontside of the substrate, and an optical stack including color filters andmicro-lens corresponding to the pixel sensors disposed over a back sideof the substrate. As the size of BSI image sensors decrease, BSI imagesensors face a number of challenges. One challenge with BSI imagesensors is cross talk between neighboring pixel sensors. As BSI imagesensors become smaller and smaller, distance between neighboring pixelsensors becomes smaller and smaller, thereby increasing the likelihoodof cross talk. Another challenge with BSI image sensors is lightcollection. Also as image sensors become smaller and smaller, thesurface area for light collection becomes smaller and smaller, therebyreducing the sensitivity of pixel sensors. This is problematic for lowlight environments. Therefore, it is in need to reduce cross talk and toincrease absorption efficiency of the pixel sensors such thatperformance and sensitivity of BSI image sensors is improved.

The present disclosure therefore provides a pixel sensor of a BSI imagesensor including a reflective grid buried in the isolation structureused to provide isolation between neighboring light-sensing devices. Insome embodiments, the present disclosure provides a hybrid isolationdisposed in the substrate, and the hybrid isolation includes thereflective grid. The reflective structure serves as a light guide or amirror that light are reflected back to the light-sensing device. Inother words, light is directed and reflected to the pixel sensor insteadof entering to the neighboring pixel sensors. Accordingly, cross talk isreduced, and thus performance and sensitivity of the pixel sensors areboth improved.

FIG. 1 is a top view of a portion of a semiconductor image sensor 100according to aspects of the present disclosure in one or moreembodiments, and FIG. 2 is a cross-sectional view of a portion of thesemiconductor image sensor 100 taken along a line A-A′ of FIG. 1according to aspects of the present disclosure in some embodiments. Insome embodiments, the semiconductor image sensor 100 is a BSI imagesensor 100. As shown in FIGS. 1 and 2 , the BSI image sensor 100includes a substrate 102, and the substrate 102 includes, for examplebut not limited to, a bulk semiconductor substrate such as a bulksilicon (Si) substrate, or a silicon-on-insulator (SOI) substrate. Thesubstrate 102 has a front side 102F and a back side 102B opposite to thefront side 102F. The BSI image sensor 100 includes a plurality of pixelsensors 110 typically arranged within an array, and each of the pixelsensors 110 includes a light-sensing device such as a photodiode 112disposed in the substrate 102. In other words, the BSI image sensor 100includes a plurality of photodiodes 112 corresponding to the pixelsensors 110. The photodiodes 112 are arranged in rows and columns in thesubstrate 102, and configured to accumulate charge (e.g. electrons) fromphotons incident thereon. Further, logic devices, such as transistors114, can be disposed over the substrate 102 on the front side 102F andconfigured to enable readout of the photodiodes 112. The pixel sensors110 are disposed to receive light with a predetermined wavelength.Accordingly, the photodiodes 112 can be operated to sense visible lightof incident light in some embodiments.

In some embodiments, a plurality of isolation structures 120 is disposedin the substrate 102 as shown in FIG. 2 . In some embodiments, theisolation structure 120 includes a deep trench isolation (DTI) and theDTI structure can be formed by the following operations. For example, afirst etch is performed from the back side 102B of the substrate 102.The first etch results in a plurality of deep trenches (not show)surrounding and between the photodiodes 112 of the pixel sensors 110. Aninsulating material such as silicon oxide (SiO) is then formed to fillthe deep trenches using any suitable deposition technique, such aschemical vapor deposition (CVD). In some embodiments, sidewalls andbottoms of the deep trenches are lined by a dielectric layer 122, suchas a coating 122 and the deep trenches are then filled up by aninsulating structure 124. The coating 122 may include a low-n material,which has a refractive index (n) less than color filter formedhereafter. The low-n material can include SiO or hafnium oxide (HfO),but the disclosure is not limited to this. In some embodiments, theinsulating structure 124 filling the deep trenches can include the low-ninsulating material. In some embodiments, a planarization is thenperformed to remove superfluous insulating material, thus the surface ofthe substrate 102 on the back side 102B is exposed, and the DTIstructures 120 surrounding and between the photodiodes 112 of the pixelsensors 110 are obtained as shown in FIG. 2 .

More importantly, a portion of the insulating structure 124 is thenremoved and thus a plurality of recesses (not shown) may be formed ineach DTI structure 120. Next, a conductive material such as tungsten(W), copper (Cu), or aluminum-copper (AlCu), or other suitable materialis formed to fill the recess. Accordingly, a conductive structure 126 isformed over the insulating structure 124 as shown in FIG. 2 . Theconductive structure 126, the insulating structure 124 and thedielectric layer 122 construct a hybrid isolation 128 surrounding eachphotodiode 112 of the pixel sensor 110. In other words, a hybridisolation 128 including the dielectric layer 122, the insulatingstructure 124 and the conductive structure 126 is provided and disposedin the substrate 102 according to some embodiments. In some embodiments,a thickness T2 of the hybrid isolation 128 is less than a thickness T1of the substrate 102. In some embodiments, the dielectric layer 122covers at least sidewalls of the conductive structure 126. Further, thedielectric layer 122 covers sidewalls and a bottom surface of theinsulating structure 124.

In some embodiments, an anti-reflective coating (ARC) 116 is disposedover the substrate 102 on the back side 102B, and a passivation layer118 is disposed over the ARC 116. In some embodiments, the ARC 116 andthe dielectric layer 122 include the same material and can be formed atthe same time. Thus a substantially flat and even surface is obtained onthe back side 102B of the substrate 102 as shown in FIG. 2 .

A back-end-of-line (BEOL) metallization stack 130 is disposed over thefront side 102F of the substrate 102. The BEOL metallization stack 130includes a plurality of metallization layers 132 stacked in aninterlayer dielectric (ILD) layer 134. One or more contacts of the BEOLmetallization stack 130 is electrically connected to the logic device114. In some embodiments, the ILD layer 134 can include a low-kdielectric material (i.e., a dielectric material with a dielectricconstant less than 3.9) or an oxide, but the disclosure is not limitedto this. The plurality of metallization layers 132 may include a metalsuch as copper (Cu), tungsten (W), or aluminum (Al), but the disclosureis not limited to this. In some embodiments, another substrate (notshown) can be disposed between the metallization structure 130 andexternal connectors such as a ball grid array (BGA) (not shown). And theBSI image sensor 100 is electrically connected to other devices orcircuits through the external connectors, but the disclosure is notlimited to this.

Referring to FIGS. 1 and 2 , in some embodiments, a plurality of colorfilters 150 corresponding to the pixel sensors 110 is disposed over thesubstrate 102 on the back side 102B. Further, another insulatingstructure 140 is disposed between the color filters 150. In someembodiments, the insulating structure 140 includes a grid structure andthe color filters 150 are located within the grid. Thus the insulatingstructure 140 surrounds each color filter 150, and separates the colorfilters 150 from each other as shown in FIGS. 1 and 2 . The insulatingstructure 140 can include materials with a refractive index less thanthe refractive index of the color filters 150 or less than a refractiveindex of Si, but the disclosure is not limited to this. Further, theconductive structure 126 is disposed between the insulating structure124 and the insulating structure 140, as shown in FIGS. 1 and 2 .

Each of the color filters 150 is disposed over each of the correspondingphotodiodes 112. The color filters 150 are assigned to correspondingcolors or wavelengths of lights, and configured to filter out all butthe assigned colors or wavelengths of lights. Typically, the colorfilters 150 assignments alternate between red, green, and blue lights,such that the color filters 150 include red color filters 150/R, greencolor filters 150/G and blue color filters 150/B, as shown in FIG. 1 .In some embodiments, the red color filters 150/R the green color filters150/G and the blue color filters 150/B are arranged in a Bayer or othermosaic pattern, but the disclosure is not limited to this.

In some embodiments, a micro-lens 160 corresponding to each pixel sensor110 is disposed over the color filter 150. It should be easilyunderstood that locations and areas of each micro-lens 160 correspond tothose of the color filter 150 or those of the pixel sensor 110 as shownin FIG. 2 .

In some embodiments, the insulating structures 124 and the dielectriclayers 122 of the hybrid isolations 128 form an isolation grid 120 inthe substrate 102, and the isolation grid 120 provides electricalisolation between neighboring pixel sensors 110. In other words, theisolation grid 120 separates the plurality of pixel sensors 110including the photodiodes 112 from each other. In some embodiments, adepth D_(I) of the isolation grid 120 is less than the thickness T1 ofthe substrate 102, as shown in FIG. 2 . In some embodiments, theconductive structures 126 of the hybrid isolations 128 form a reflectivegrid 126 disposed over the isolation grid 120 on the back side 102B ofthe substrate 102. In some embodiments, the depth D_(I) of the isolationgrid 120 is less than the thickness T1 of the substrate 102, and a depthD_(R) of the reflective grid 126 is less than the depth D_(I) of theisolation grid 120. It should be noted that depth D_(R) of thereflective grid 126 is related to a pitch P of the pixel sensor 110. Forexample but not limited to, the depth D_(R) of the reflective grid 126can be greater than 0.1 micrometer (μm) and less than the depth D_(I) ofthe isolation grid 120 when the pitch P of the pixel sensor 110 is about0.9 μm. In some embodiments, the depth D_(R) of the reflective grid 126can be greater than 0.2 μm and less than the depth D_(I) of theisolation grid 120 when the pitch P of the pixel sensor 110 is about 0.7μm. In some embodiments, the insulating structures 140 between the colorfilters 150 form a low-n grid 140 over the substrate 102 on the backside 102B. Thus, the low-n grid 140 separates the color filters 150 fromeach other. As shown in FIG. 2 , the reflective grid 126 is disposedbetween the low-n grid 140 and the isolation grid 120. Further, thelow-n grid 140 overlaps the reflective grid 126 and the isolation grid120 from a plan view, in some embodiments.

Due to the low refractive index, the low-n grid 140 serves as a lightguide to direct or reflect light to the color filters 150. Consequently,the low-n structure 140 effectively increases the amount of the lightincident into the color filters 150. Further, due to the low refractiveindex, the low-n grid 140 provides optical isolation between neighboringcolor filters 150. The reflective grid 126 serves as a light guide or amirror, and reflects light to the photodiode 112. Consequently, thereflective grid 126 effectively increases the amount of light to beabsorbed by photodiode 112 and thus provides optical isolation betweenneighboring pixel sensors 110. On the other hands, the isolation grid120 including the dielectric layer 122 and the insulating structure 124provides electrical isolation between the neighboring pixel sensors 110.In other words, the isolation grid 120 separates the plurality of pixelsensors 110 including the photodiodes 112 from each other therebyserving as a substrate isolation grid and reducing cross-talk.

FIG. 3 is a cross-sectional view of a portion of a semiconductor imagesensor 200 according to aspects of the present disclosure in one or moreembodiments. It should be easily understood elements the same in the BSIimage sensor 100 and the BSI image sensor 200 can include the samematerial and/or formed by the same operations, and thus those detailsare omitted in the interest of brevity. In some embodiments, thesemiconductor image sensor 200 is a BSI image sensor 200. In someembodiments, a top view of the BSI images sensor 200 can be similar asshown FIG. 1 , but the disclosure is not limited to this. As shown inFIG. 3 , the BSI image sensor 200 includes a substrate 202, and thesubstrate 202 has a front side 202F and a back side 202B opposite to thefront side 202F. The BSI image sensor 200 includes a plurality of pixelsensors 210 typically arranged within an array. A plurality ofphoto-sensing devices such as photodiodes 212 corresponding to the pixelsensors 210 is disposed in the substrate 202. The photodiodes 212 arearranged in rows and columns in the substrate 202. In other words, eachof the pixel sensors 210 includes a photo-sensing device such as thephotodiode 212. Further, logic devices, such as transistors 214, aredisposed over the front side 202F of the substrate 202 and configured toenable readout of the photodiodes 212.

A plurality of isolation structures 220 is disposed in the substrate 202as shown in FIG. 3 . In some embodiments, the isolation structure 220includes a DTI structure and the DTI structure can be formed byoperations as mentioned above. Therefore, those details are omitted inthe interest of brevity. In some embodiments, sidewalls and bottoms ofthe deep trenches are lined by a dielectric layer 222, such as a coating222 and the deep trenches are then filled up by an insulating structure224. As mentioned above, the coating 222 may include a low-n material,which has a refractive index (n) less than color filter formedhereafter. The low-n material can include SiO or hafnium oxide (HfO),but the disclosure is not limited to this. In some embodiments, theinsulating structure 224 filling the deep trenches can include the low-ninsulating material. A planarization is then performed to removesuperfluous insulating material, thus the surface of the substrate 202on the back side 202B is exposed, and the DTI structures 220 surroundingand between the photodiodes 212 of the pixel sensors 210 are obtained asshown in FIG. 3 .

More importantly, a portion of the insulating structure 224 is thenremoved and thus a recess (not shown) may be formed in each DTIstructure 220. Next, a conductive material such as W, Cu, or AlCu, orother suitable material is formed to fill the recess. Accordingly, aconductive structure 226 is formed over the insulating structure 224.The conductive structure 226, the insulating structure 224 and thedielectric layer 222 construct a hybrid isolation 228 surrounding eachphotodiode 212 of the pixel sensor 210. In other words, a hybridisolation 228 including the dielectric layer 222, the insulatingstructure 224 and the conductive structure 226 is provided and disposedin the substrate 202 according to some embodiments. In some embodiments,a thickness T2 of the hybrid isolation 228 is substantially equal to athickness T1 of the substrate 202. In some embodiments, the dielectriclayer 222 covers at least sidewalls of the conductive structure 226.Further, the dielectric layer 222 covers sidewalls and a bottom surfaceof the insulating structure 224.

In some embodiments, an ARC 216 is disposed over the substrate 202 onthe back side 202B, and a passivation layer 218 is disposed over the ARC216. In some embodiments, the ARC 216 and the dielectric layer 222include the same material and can be formed at the same time. Thus asubstantially flat and even surface is obtained on the back side 202B ofthe substrate 202 as shown in FIG. 3 .

A BEOL metallization stack 230 is disposed over the front side 202F ofthe substrate 202. As mentioned above the BEOL metallization stack 230includes a plurality of metallization layers 232 stacked in an ILD layer234. One or more contacts of the BEOL metallization stack 230 areelectrically connected to the logic device 214. In some embodiments,another substrate (not shown) can be disposed between the metallizationstructure 230 and external connectors such as a ball grid array (BGA)(not shown). And the BSI image sensor 200 is electrically connected toother devices or circuits through the external connectors, but thedisclosure is not limited to this.

Referring to FIG. 3 , in some embodiments, a plurality of color filters250 corresponding to the pixel sensors 210 is disposed over the pixelsensors 210 on the back side 202B of the substrate 202. Further, anotherinsulating structure 240 is disposed between the color filters 250. Insome embodiments, the insulating structure 240 includes a grid structureand the color filters 250 are located within the grid. Thus theinsulating structure 240 surrounds each color filter 250, and separatesthe color filters 250 from each other as shown in FIG. 3 . Theinsulating structure 240 can include materials with a refractive indexless than the refractive index of the color filters 250 or a materialwith a refractive index less than a refractive index of Si, but thedisclosure is not limited to this. Further, the conductive structure 226is disposed between the insulating structure 224 and the insulatingstructure 240, as shown in FIG. 3 .

As mentioned above, each of the color filters 250 is disposed over eachof the corresponding photodiodes 212. The color filters 250 are assignedto corresponding colors or wavelengths of lights, and configured tofilter out all but the assigned colors or wavelengths of lights.Typically, the color filters 250 assignments alternate between red,green, and blue lights, such that the color filters 250 include redcolor filters, green color filters and blue color filters. In someembodiments, the red color filters, the green color filters and the bluecolor filters are arranged in a Bayer or other mosaic pattern, but thedisclosure is not limited to this. In some embodiments, a micro-lens 260corresponding to each pixel sensor 210 is disposed over the color filter250. It should be easily understood that locations and areas of eachmicro-lens 260 correspond to those of the color filter 250 or those ofthe pixel sensor 210 as shown in FIG. 3 .

In some embodiments, the insulating structures 224 and the dielectriclayers 222 of the hybrid isolations 228 form an isolation grid 220 inthe substrate 202, and the isolation grid 220 provides electricalisolation between neighboring pixel sensors 210. In other words, theisolation grid 220 separates the plurality of pixel sensors 210including the photodiodes 212 from each other. In some embodiments, adepth D_(I) of the isolation grid 220 is less than the thickness T1 ofthe substrate 202, as shown in FIG. 3 . In some embodiments, theconductive structures 226 of the hybrid isolations 228 form a reflectivegrid 226 disposed over the isolation grid 220 on the back side 202B ofthe substrate 202. In some embodiments, a depth D_(I) of the isolationgrid 220 is substantially equal to the thickness T1 of the substrate202, and a depth D_(R) of the reflective grid 226 is less than the depthD_(I) of the isolation grid 220. As mentioned above, the depth D_(R) ofthe reflective grid 226 is related to a pitch P of the pixel sensor 210.In some embodiments, the insulating structures 240 between the colorfilters 250 form a low-n grid 240 over the substrate 202 on the backside 202B. Thus, the low-n grid 240 separates the color filters 250 fromeach other. As shown in FIG. 3 , the reflective grid 226 is disposedbetween the low-n grid 240 and the isolation grid 220. Further, thelow-n grid 240 overlaps the reflective grid 226 and the isolation grid220 from a plan view, in some embodiments.

Due to the low refractive index, the low-n grid 240 serves as a lightguide to direct or reflect light to the color filters 250. Consequently,the low-n structure 240 effectively increases the amount of the lightincident into the color filters 250. Further, due to the low refractiveindex, the low-n grid 240 provides optical isolation between neighboringcolor filters 250. The reflective grid 226 serves as a light guide or amirror, and reflects light to the photodiode 212. Consequently, thereflective grid 226 effectively increases the amount of light to beabsorbed by photodiode 212 and thus provides optical isolation betweenneighboring pixel sensors 210. On the other hands, the isolation grid220 including the dielectric layer 222 and the insulating structure 224provides electrical isolation between the neighboring pixel sensors 210.In other words, the isolation grid 220 separates the plurality of pixelsensors 210 including the photodiodes 212 from each other therebyserving as a substrate isolation grid and reducing cross-talk.

FIG. 4 is a cross-sectional view of a portion of a BSI image sensor 300according to aspects of the present disclosure in one or moreembodiments. It should be easily understood elements the same in the BSIimage sensors 100/200 and the BSI image sensor 300 can include the samematerial and/or formed by the same operations, and thus those detailsare omitted in the interest of brevity. In some embodiments, thesemiconductor image sensor 300 is a BSI image sensor 300. In someembodiments, a top view of the BSI images sensor 300 can be similar asshown FIG. 1 , but the disclosure is not limited to this. As shown inFIG. 4 , the BSI image sensor 300 includes a substrate 302, and thesubstrate 302 has a front side 302F and a back side 302B opposite to thefront side 302F. The BSI image sensor 300 includes a plurality of pixelsensors 310 typically arranged within an array. A plurality ofphoto-sensing devices such as photodiodes 312 corresponding to the pixelsensors 310 is disposed in the substrate 302. The photodiodes 312 arearranged in rows and columns in the substrate 302. In other words, eachof the pixel sensors 310 includes a photo-sensing device such as thephotodiode 312. Further, logic devices, such as transistors 314, aredisposed over the front side 302F of the substrate 302 and configured toenable readout of the photodiodes 312.

A hybrid isolation 328 is disposed in the substrate 302 as shown in FIG.4 . In some embodiments, the hybrid isolation 328 can be formed byoperations for forming DTI structure, but the disclosure is not limitedto this. For example, a first etch is performed from the back side 302Bof the substrate 302. The first etch results in a plurality of deeptrenches (not show) surrounding and between the photodiodes 312. In someembodiments, sidewalls and bottoms of the deep trenches are lined by adielectric layer 322, such as a coating 322. The coating 322 may includea low-n material, which has a refractive index less than color filterformed hereafter. Next, a conductive material such as W, Cu, AlCu, orother suitable material is formed to fill the trenches. Accordingly, aconductive structure 326 is disposed in each deep trench. The conductivestructure 326 and the dielectric layer 322 construct the hybridisolation 328. In other words, a hybrid isolation 328 including thedielectric layer 322 and the conductive structure 326 is provided anddisposed in the substrate 302 according to some embodiments. In someembodiments, a thickness T2 of the hybrid isolation 328 is substantiallyequal to a thickness T1 of the substrate 302. Further, the dielectriclayer 322 covers sidewalls and a bottom surface of the conductivestructure 326, as shown in FIG. 4 .

In some embodiments, an ARC 316 is disposed over the substrate 302 onthe back side 302B, and a passivation layer 318 is disposed over the ARC316. In some embodiments, the ARC 316 and the dielectric layer 322include the same material and can be formed at the same time. Thus asubstantially flat and even surface is obtained on the back side 302B ofthe substrate 302 as shown in FIG. 4 .

A BEOL metallization stack 330 is disposed over the front side 302F ofthe substrate 302. As mentioned above, the BEOL metallization stack 330includes a plurality of metallization layers 332 stacked in an ILD layer334. One or more contacts of the BEOL metallization stack 330 areelectrically connected to the logic device 314. In some embodiments,another substrate (not shown) can be disposed between the metallizationstructure 330 and external connectors such as a ball grid array (BGA)(not shown). And the BSI image sensor 300 is electrically connected toother devices or circuits through the external connectors, but thedisclosure is not limited to this.

Referring to FIG. 4 , in some embodiments, a plurality of color filters350 corresponding to the pixel sensors 310 is disposed over the pixelsensors 310 on the back side 302B of the substrate 302. Further, aninsulating structure 340 is disposed between the color filters 350. Insome embodiments, the insulating structure 340 includes a grid structureand the color filters 350 are located within the grid. Thus theinsulating structure 340 surrounds each color filter 350, and separatesthe color filters 350 from each other as shown in FIG. 4 . Theinsulating structure 340 can include materials with a refractive indexless than the refractive index of the color filters 350 or a materialwith a refractive index less than a refractive index of Si, but thedisclosure is not limited to this.

As mentioned above, each of the color filters 350 is disposed over eachof the corresponding photodiodes 312. The color filters 350 are assignedto corresponding colors or wavelengths of lights, and configured tofilter out all but the assigned colors or wavelengths of lights.Typically, the color filters 350 assignments alternate between red,green, and blue lights, such that the color filters 350 include redcolor filters, green color filters and blue color filters. In someembodiments, the red color filters, the green color filters and the bluecolor filters are arranged in a Bayer or other mosaic pattern, but thedisclosure is not limited to this. In some embodiments, a micro-lens 360corresponding to each pixel sensor 310 is disposed over the color filter350. It should be easily understood that locations and areas of eachmicro-lens 360 correspond to those of the color filter 350 or those ofthe pixel sensor 310 as shown in FIG. 4 .

In some embodiments, the dielectric layers 322 of the hybrid isolations328 form an isolation grid 320 in the substrate 302, and the isolationgrid 320 provides electrical isolation between neighboring pixel sensors310. In some embodiments, a depth D_(I) of the isolation grid 320 issubstantially equal to the thickness T1 of the substrate 302, as shownin FIG. 4 . In some embodiments, the conductive structures 326 of thehybrid isolations 328 form a reflective grid 326 disposed in thesubstrate 302. In some embodiments, a depth D_(I) of the isolation grid320 is substantially equal to the thickness T1 of the substrate 302, anda depth D_(R) of the reflective grid 326 is less than the depth D_(I) ofthe isolation grid 320. As mentioned above, the depth D_(R) of thereflective grid 326 is related to a pitch P of the pixel sensor 310. Insome embodiments, the insulating structures 340 between the colorfilters 350 form a low-n grid 340 over the substrate 302 on the backside 302B. As shown in FIG. 4 , the reflective grid 326 is disposedbetween the low-n grid 340 and the isolation grid 320. Further, thelow-n grid 340 overlaps the reflective grid 326 from a plan view, insome embodiments.

Due to the low refractive index, the low-n grid 340 serves as a lightguide to direct or reflect light to the color filters 350. Consequently,the low-n structure 340 effectively increases the amount of the lightincident into the color filters 350. Further, due to the low refractiveindex, the low-n grid 340 provides optical isolation between neighboringcolor filters 350. The reflective grid 326 serves as a light guide or amirror, and reflects light to the photodiode 312. Consequently, thereflective grid 326 effectively increases the amount of light to beabsorbed by photodiode 312 and thus provides optical isolation betweenneighboring pixel sensors 310. On the other hands, the isolation grid320 including the dielectric layer 322 provides electrical isolationbetween the neighboring pixel sensors 310. In other words, the isolationgrid 320 separates the plurality of pixel sensors 310 including thephotodiodes 312 from each other thereby serving as a substrate isolationgrid and reducing cross-talk.

FIG. 5 is a cross-sectional view of a portion of a BSI image sensor 400according to aspects of the present disclosure in one or moreembodiments. It should be noted that the same elements in the BSI imagesensor 400 and the BSI image sensor 100/200/300 can include the samematerial and/or formed by the same operations, and thus those detailsare omitted in the interest of brevity. In some embodiments, thesemiconductor image sensor 400 is a BSI image sensor 400. In someembodiments, a top view of the BSI images sensor 400 can be similar asshown FIG. 1 , but the disclosure is not limited to this. As shown inFIG. 5 , the BSI image sensor 400 includes a substrate 402. Thesubstrate 402 has a front side 402F and a back side 402B opposite to thefront side 402F. The BSI image sensor 400 includes a plurality of pixelsensors 410 typically arranged within an array, and each of the pixelsensors 410 includes a light-sensing device such as a photodiode 412disposed in the substrate 402. In other words, the BSI image sensor 400includes a plurality of photodiodes 412 corresponding to the pixelsensors 410. The photodiodes 412 are arranged in rows and columns in thesubstrate 402, and configured to accumulate charge (e.g. electrons) fromphotons incident thereon. Further, logic devices, such as transistors414, can be disposed over the substrate 402 on the front side 402F andconfigured to enable readout of the photodiodes 412. The pixel sensors410 are disposed to receive light with a predetermined wavelength.Accordingly, the photodiodes 412 can be operated to sense visible lightof incident light in some embodiments.

A plurality of isolation structures 420 is disposed in the substrate 402as shown in FIG. 5 . In some embodiments, the isolation structure 420includes a DTI structure, and the DTI structure can be formed byoperations as mentioned above, therefore those details are omitted forbrevity. In some embodiments, sidewalls and bottoms of the deep trenchesare lined by a dielectric layer 422, such as a coating 422 and the deeptrenches are then filled up by an insulating structure 424. The coating422 may include a low-n material, which has a refractive index (n) lessthan color filter formed hereafter. In some embodiments, the insulatingstructure 424 filling the deep trenches can include the low-n insulatingmaterial. A planarization is then performed to remove superfluousinsulating material, thus the surface of the substrate 402 on the backside 402B is exposed, and the DTI structures 420 surrounding and betweenthe photodiodes 412 are obtained.

In some embodiments, a portion of the insulating structure 424 is thenremoved and thus a recess (not shown) may be formed in each DTIstructure 420. Next, a conductive material is formed to fill the recess.Accordingly, a conductive structure 426 is formed over the insulatingstructure 424 as shown in FIG. 5 . The conductive structure 426, theinsulating structure 424 and the dielectric layer 422 construct a hybridisolation 428. In other words, a hybrid isolation 428 including thedielectric layer 422, the insulating structure 424 and the conductivestructure 426 is provided and disposed in the substrate 402 according tosome embodiments. In some embodiments, a depth or a thickness T2 of thehybrid isolation 428 is less than the thickness T1 of the substrate 402.However, in some embodiments the depth or the thickness T2 of the hybridisolation 428 can be substantially equal to the thickness T1 of thesubstrate 402. Such hybrid isolation 428 can be similar as the hybridisolation 228 shown in FIG. 3 , therefore those details are omitted inthe interest of brevity. In those embodiments, the dielectric layer 422covers at least sidewalls of the conductive structure 426. Further, thedielectric layer 422 covers sidewalls of the insulating structure 424and a bottom surface of the insulating structure 424.

However, in some embodiments, the conductive structure 426 can be formedto fill the deep trenches directly after forming the dielectric layer422. Consequently, a hybrid isolation 428 including the dielectric layer422 and the conductive structure 426 can be obtained as shown in FIG. 5. In those embodiments, the dielectric layer 422 covers not only thesidewalls of the conductive structure 426 but also the bottom surface ofthe conductive structure 426. Such hybrid isolation 428 can be similaras hybrid isolation 328 shown in FIG. 4 , therefore those details areomitted in the interest of brevity.

In some embodiments, an ARC 416 is disposed over the substrate 402 onthe back side 402B, and a passivation layer 418 is disposed over the ARC416. In some embodiments, the ARC 416 and the dielectric layer 422include the same material and can be formed at the same time. Thus asubstantially flat and even surface is obtained on the back side 402B ofthe substrate 402 as shown in FIG. 5 .

As mentioned above, a BEOL metallization stack 430 is disposed over thefront side 402F of the substrate 402. The BEOL metallization stack 430includes a plurality of metallization layers 432 stacked in an ILD layer434. One or more contacts of the BEOL metallization stack 430 areelectrically connected to the logic device 414. In some embodiments,another substrate (not shown) can be disposed between the metallizationstructure 430 and external connectors such as a ball grid array (BGA)(not shown). And the BSI image sensor 400 is electrically connected toother devices or circuits through the external connectors, but thedisclosure is not limited to this.

Referring to FIG. 5 , in some embodiments, a plurality of color filters450 corresponding to the pixel sensors 410 is disposed over the pixelsensors 410 on the back side 402B of the substrate 402. Further, ahybrid isolation 440 is disposed between the color filters 450 in someembodiments. In some embodiments, the hybrid isolation 440 includes agrid structure and the color filters 450 are located within the grid.Thus the hybrid isolation 440 surrounds the color filter 450, andseparates the color filters 450 from each other as shown in FIG. 5 . Thehybrid isolation 440 can include layers with a refractive index lessthan the refractive index of the color filters 450. In some embodiments,the composite structure 440 can include a composite stack including atleast a conductive structure 442 and an insulating structure 444disposed over the conductive structure 442. In some embodiments, theconductive structure 442 can include W, Cu, or AlCu, and the insulatingstructure 444 includes a material with a refractive index less than therefractive index of the color filter 450 or a material with a refractiveindex less than a refractive index of Si, but the disclosure is notlimited to this.

Each of the color filters 450 is disposed over each of the correspondingphotodiodes 412. The color filters 450 are assigned to correspondingcolors or wavelengths of lights, and configured to filter out all butthe assigned colors or wavelengths of lights. Typically, the colorfilters 450 assignments alternate between red, green, and blue lights,such that the color filters 450 include red color filters, green colorfilters and blue color filters. In some embodiments, the red colorfilters, the green color filters and the blue color filters are arrangedin a Bayer mosaic pattern, but the disclosure is not limited to this. Insome embodiments, a micro-lens 460 corresponding to each pixel sensor410 is disposed over the color filter 450. It should be easilyunderstood that locations and areas of each micro-lens 460 correspond tothose of the color filter 450 or those of the pixel sensor 410 as shownin FIG. 5 .

In some embodiments, the hybrid isolation 428 including the insulatingstructures 424, the dielectric layers 422 and the conductive structures426 is disposed in the substrate 402. The insulating structures 424and/or the dielectric layers 422 of the hybrid isolation 428 provideelectrical isolation between neighboring pixel sensors 410. In otherwords, insulating structures 424 and/or the dielectric layers 422 of thehybrid isolation 428 serve as a substrate isolation grid separating theplurality of pixel sensors 410 including the photodiodes 412 from eachother, and thus reducing cross-talk. A depth T2 of the hybrid isolation428 can be equal to or less than the thickness T1 of the substrate 402,as shown in FIG. 5 . In some embodiments, the conductive structures 426of the hybrid isolation 428 form a reflective grid. In some embodiments,a depth D_(R) of the reflective grid 426 can be equal to or less thanthe depth T2 of the hybrid isolation 428. As mentioned above, the depthD_(R) of the reflective grid 426 is related to a pitch P of the pixelsensor 410. Additionally, the dielectric layers 422 and/or theinsulating structures 424 form an isolation grid 420, and the reflectivegrid 426 is disposed between the isolation grid 420 and the hybridisolation 440 including the conductive structure 442 and the insulatingstructure 444, as shown in FIG. 5 . Further, the hybrid isolation 440overlaps the hybrid isolation 428 from a plan view.

Due to the low refractive index, the hybrid isolation 440 serves as alight guide to direct or reflect light to the color filters 450.Consequently, the hybrid isolation 440 effectively increases the amountof the light incident into the color filters 450. Further, due to thelow refractive index, the hybrid isolation 440 provides opticalisolation between neighboring color filters 450. The conductivestructure 426 of the hybrid isolation 428 serves as a light guide or amirror, and reflects light to the photodiode 412. Consequently, theconductive structure/reflective grid 426 effectively increases theamount of light to be absorbed by photodiode 412 and thus providesoptical isolation between neighboring pixel sensors 410. On the otherhands, the isolation grid 420 (including the conductive structure 424and the dielectric layer 422 of the hybrid isolation 428) provideselectrical isolation between the neighboring pixel sensors 410.

Please refer to FIG. 6 and FIGS. 7A-7H. FIG. 6 shows a flow chartrepresenting method for forming a semiconductor image sensor accordingto aspects of the present disclosure, and FIGS. 7A-7H are a series ofcross-sectional views of a semiconductor image sensor at variousfabrication stages constructed according to aspects of the presentdisclosure in one or more embodiments. In the present disclosure, amethod of manufacturing a semiconductor image sensor 50 is alsodisclosed. In some embodiments, a semiconductor image sensor structure600 can be formed by the method 50. The method 50 includes a number ofoperations and the description and illustration are not deemed as alimitation as the sequence of the operations. The method 50 includes anumber of operations (502, 504, 506, 508, and 510). Additionally, itshould be noted that elements the same in FIGS. 2 and 7A-7H aredesignated by the same numerals, and can include the same materials,thus those details are omitted in the interest of brevity.

In operation 502, a substrate 602 is provided or received. As mentionedabove, the substrate 602 has a front side 602F and a back side 602Bopposite to the front side 102F. The semiconductor image sensor 600includes a plurality of pixel sensors 610 typically arranged within anarray, and each of the pixel sensors 610 includes a light-sensing devicesuch as a photodiode 612 disposed in the substrate 602. Further, logicdevices, such as a transistor 614, can be disposed over the substrate602 on the front side 602F and configured to enable readout of thephotodiodes 612. The pixel sensors 610 are disposed to receive lightwith a predetermined wavelength. As mentioned above, the photodiodes 612can be operated to sense visible light of incident light in someembodiments.

In some embodiments, a BEOL metallization stack 630 is disposed over thefront side 602F of the substrate 602. The BEOL metallization stack 630includes a plurality of metallization layers 632 stacked in an ILD layer634. One or more contacts of the BEOL metallization stack 630 iselectrically connected to the logic device 614. In some embodiments,another substrate (not shown) can be disposed between the metallizationstructure 630 and external connectors such as a ball grid array (BGA)(not shown). And the BSI image sensor 600 is electrically connected toother devices or circuits through the external connectors, but thedisclosure is not limited to this.

In operation 504, a first etch is performed from the back side 602B ofthe substrate 602. The first etch results in a plurality of deeptrenches 613 surrounding and between the photodiodes 612 of the pixelsensors 610, as shown in FIG. 7A.

In operation 506, a plurality of hybrid isolation structures 620 isformed in the deep trenches 613. In some embodiment, the forming of thehybrid isolation structures 620 further includes following operations.Referring to FIG. 7B, sidewalls and bottoms of the deep trenches 613 arelined by a dielectric layer 622, such as a coating 622. In someembodiments, the coating 622 may include a low-n material, which has arefractive index (n) less than color filter formed hereafter. The low-nmaterial can include SiO or HfO, but the disclosure is not limited tothis.

Referring to FIG. 7C, an insulating material 624 such as SiO is thenformed to fill the deep trenches 613 using any suitable depositiontechnique, such as CVD. In some embodiments, the insulating structure624 filling the deep trenches can include the low-n insulating material.

Referring to FIG. 7D, in some embodiments, the insulating material 624is then recessed from the back side 602B of the substrate 602.Consequently, a plurality of DTI structures 620 surrounding and betweenthe photodiodes 612 of the pixel sensors 610 are obtained as shown inFIG. 7D. Further, a plurality of recesses 615 is formed in each DTIstructure 620.

Referring to FIG. 7E, Next, a conductive material 626 such as W, Cu, orAlCu, or other suitable material is formed to fill the recesses 613.Accordingly, a conductive structure 626 is formed over the insulatingstructure 624 as shown in FIG. 7E. Referring to FIG. 7F, a planarizationthen can be performed to remove the superfluous conductive material 626,such that top surfaces of the insulating materials 624 are exposed fromthe back side 602B of the substrate 602. Accordingly, the conductivestructure 626, the insulating structure 624 and the dielectric layer 622construct the hybrid isolations 628 surrounding each photodiode 612 ofthe pixel sensor 610. In some embodiments, an ARC and a passivationlayer (not shown) can be disposed over the insulating material 624. Thusa substantially flat and even surface is obtained on the back side 602Bof the substrate 602.

In operation 508, an insulating structure 640 including a grid structureis formed over the back side 602B of the substrate 602, as shown in FIG.7G. In some embodiments, the insulating structure 640 can includematerials with a refractive index less than the refractive index of thecolor filters to be formed or less than a refractive index of Si, butthe disclosure is not limited to this.

In operation 510, a plurality of color filters 650 are disposed withinthe grid of the insulating structure 640. Thus the insulating structure640 surrounds each color filter 650, and separates the color filters 650from each other as shown in FIG. 7H. Further, the conductive structures626 are disposed between the insulating structures 624 and theinsulating structure 640, as shown in FIG. 7H. In some embodiments, aplurality of micro-lenses 660 corresponding to each pixel sensor 610 isdisposed over the color filters 650. It should be easily understood thatlocations and areas of each micro-lens 660 correspond to those of thecolor filter 650 or those of the pixel sensor 610 as shown in FIG. 7H.

Accordingly, the present disclosure therefore provides a BSI imagesensor including at least a hybrid isolation disposed in the substrate.The hybrid isolation includes at least a conductive structure and adielectric layer. In some embodiments, the hybrid isolation includes aninsulating structure under the conductive structure. Further, theinsulating structures and/or the dielectric layers form an isolationgrid providing electrical isolation between neighboring pixel sensors,while the conductive structures form a reflective grid providing opticalisolation between neighboring photodiodes. And a low-n structure oranother hybrid isolation providing optical isolation between neighboringcolor filters can be formed over the substrate on the back side.Accordingly, cross-talk between neighboring pixel sensors andsignal-to-noise ratio (SNR) are reduced. Further, quantum efficiency andangular response are improved. Consequently, the sensitivity of the BSIimage sensor is improved.

In some embodiments, a BSI image sensor is provided. The BSI imagesensor includes a substrate including a front side and a back sideopposite to the front side, a plurality of pixel sensors, an isolationgrid disposed in the substrate and separating the plurality of pixelsensors from each other, a reflective grid disposed over the isolationgrid on the back side of the substrate, an a low-n grid disposed overthe back side of the substrate and overlapping the reflective grid froma top view. In some embodiments, a width of the low-n grid is greaterthan a width of the reflective grid.

In some embodiments, a BSI image sensor is provided. The BSI imagesensor includes a substrate, a pixel sensor, and a hybrid isolationsurrounding the pixel sensor in the substrate. The hybrid isolationincludes a conductive structure and a first insulating structuredisposed in the substrate. In some embodiments, a thickness of theconductive structure is greater than a thickness of the first insulatingstructure.

In some embodiments, a BSI image sensor is provided. The BSI imagesensor includes a substrate including a front side and a back sideopposite to the front side, a pixel sensor, a color filter correspondingto the pixel sensor and disposed over the substrate on the back side, afirst insulating structure disposed in the substrate and surrounding thepixel sensor, a first conductive structure disposed in the substrate andover the first insulating structure on the back side of the substrateand surrounding the pixel sensor, a second insulating structuresurrounding the color filter on the back side of the substrate, and asecond conductive structure surrounding the color filter on the backside of the substrate. In some embodiments, the first conductivestructure and the second conductive structure are between the firstinsulating structure and the second insulating layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein.

What is claimed is:
 1. A back side illumination (BSI) image sensorcomprising: a substrate comprising a front side and a back side oppositeto the front side; a plurality of pixel sensors; a first isolation griddisposed in the substrate and separating the plurality of pixel sensorsfrom each other; a first reflective grid disposed over the firstisolation grid on the back side of the substrate; a dielectric layercovering sidewalls of the first isolation grid and sidewalls of thefirst reflective grid; a second isolation grid disposed over the backside of the substrate and overlapping the reflective grid from a planview; and a second reflective grid disposed between the second isolationgrid and the substrate, wherein a width of the second isolation grid isgreater than a width of the first reflective grid.
 2. The BSI imagesensor of claim 1, further comprising a plurality of color filtersdisposed over the substrate on the back side.
 3. The BSI image sensor ofclaim 2, wherein the second isolation grid and the second reflectivegrid are disposed between and separating the color filters from eachother.
 4. The BSI image sensor of claim 1, wherein the first reflectivegrid is disposed between the second reflective grid and the firstisolation grid.
 5. The BSI image sensor of claim 1, wherein the secondisolation grid comprises an insulating material.
 6. The BSI image sensorof claim 1, wherein the first isolation grid comprises at least aninsulating material.
 7. The BSI image sensor of claim 1, wherein thefirst reflective grid comprises a conductive material.
 8. The BSI imagesensor of claim 1, wherein a depth of the first isolation grid is equalto or less than a thickness of the substrate.
 9. The BSI image sensor ofclaim 1, wherein the second isolation grid and the second reflectivegrid are separated from the first reflective grid.
 10. The BSI imagesensor of claim 1, wherein the second isolation grid and the secondreflective grid are in contact with the first reflective grid.
 11. Aback side illumination (BSI) image sensor comprising: a substratecomprising a front side and a back side opposite to the front side; apixel sensor; a first hybrid isolation surrounding the pixel sensor inthe substrate, and the first hybrid isolation comprising: a reflectivegrid disposed in the substrate; a first isolation grid disposed in thesubstrate; and a dielectric layer covering sidewalls of the reflectivegrid and sidewalls of the first isolation structure; and a second hybridgrid disposed over the back side of the substrate and overlapping thereflective grid from a plan view, wherein a thickness of the reflectivegrid is greater than a thickness of the first isolation grid.
 12. TheBSI image sensor of claim 11, wherein a thickness of the first hybridisolation is equal to a thickness of the substrate.
 13. The BSI imagesensor of claim 11, wherein the dielectric layer covers a bottom surfaceof the first isolation grid.
 14. The BSI image sensor of claim 11,wherein the second hybrid grid comprises a second isolation griddisposed over the substrate on the back side.
 15. The BSI image sensorof claim 14, wherein the reflective grid is disposed between the firstisolation grid and the second isolation grid.
 16. A back sideillumination (BSI) image sensor comprising: a substrate comprising afront side and a back side opposite to the front side; a pixel sensor; acolor filter corresponding to the pixel sensor and disposed over thesubstrate on the back side; a first isolation grid disposed in thesubstrate and surrounding the pixel sensor; a first reflective griddisposed in the substrate and surrounding the pixel sensor; a dielectriclayer covering sidewalls of the first isolation grid and sidewalls ofthe first reflective grid; a second isolation grid surrounding the colorfilter on the back side of the substrate; and a second reflective gridsurrounding the color filter on the back side of the substrate, whereinthe second reflective grid and the first reflective grid and are betweenthe second isolation grid and the first isolation grid.
 17. The BSIimage sensor of claim 16, wherein the dielectric layer covers a bottomsurface of the first isolation grid.
 18. The BSI image sensor of claim16, wherein the second isolation grid covers sidewalls and a top surfaceof the second reflective grid.
 19. The BSI image sensor of claim 16,wherein the first reflective grid is separated from the secondreflective grid.
 20. The BSI image sensor of claim 16, wherein the firstisolation grid, the first reflective grid, the second isolation grid andthe second reflective grid are aligned with each other.